The use of ophthalmic lenses for the correction of ametropia is well known. In the manufacture of spectacle lenses, it is desirable to use high refractive index materials, or materials with a refractive index greater than 1.50, in order to provide acceptable edge and center thicknesses, especially in higher power lenses. However, increasing the refractive index using conventional materials such as polycarbonate or inorganic glass results in an increase in chromatic aberration or color dispersion.
Longitudinal and transverse chromatic aberration is caused by the displacement of images formed by light of different wavelengths. The magnitude of the aberration depends on the power of the lens and the physical properties of the lens material. Persons wearing spectacle lenses made of conventional materials will experience chromatic aberration to varying degrees, especially in the periphery of their visual fields.
For a refractive single element lens, typical for a spectacle lens, the lens' transverse chromatic aberration (“TCA”) in diopters depends upon the Abbe number (V), the lens power(Φ) in diopters, and the gaze height on the lens from the lens center (y) in millimeters as shown in Equation I.                     TCA        =                  0.1          ·          y          ·                      Φ            V                                              (        I        )            The following table shows the TCA for various lens powers and Abbe values at a gaze height of 15 mm.
TABLE 1Transverse Chromatic Aberration in DioptersLens Power in DioptersAbbe Value - V12345678910250.060.120.180.240.300.360.420.480.540.60300.050.100.150.200.250.300.350.400.450.50350.040.090.130.170.210.260.300.340.390.43400.040.080.110.150.190.230.260.300.340.38450.030.070.100.130.170.200.230.270.300.33500.030.060.090.120.150.180.210.240.270.30550.030.050.080.110.140.160.190.220.250.27600.030.050.080.100.130.150.180.200.230.25The TCA becomes problematic to many wearers if it is greater than 0.25 diopters.
Typical conventional high refractive index materials have Abbe numbers from 30 to 45, which will cause problems for some wearers. Some low refractive index materials that are considered low dispersion will have Abbe numbers greater than 55, which gives acceptable chromatic performance to the vast majority of wearers. However, high refractive index materials are desirable for spectacle lenses because they permit production of thinner and lighter weight lenses. Therefore, a need exists for a high refractive index material for spectacle lens use that can provide chromatic performance equivalent to low refractive index lenses with large Abbe numbers.